Method of electrolytic production of perchloric acid.



E. C. WALKER, 3D.

METHOD OF ELECTROLYTIC PRODUCTION OF PERCHLORIC ACID.

APPLICATION FlLED APR. 23. 1917.

l ,2? 1,633. Patented July 9, 1918.

/ kflorwe gks.

EDWARD c. WALKER, 3D, or

ED STATES PA orrrcn.

BROOKLINE, mssacriusnr'rs.

METHOD OF ELECTROLYTIC PRODUCTION OF' PERGHLORIC ACID.

Application filed April 23, 1917. Serial lilo-163.760.

To all whom it may concern:

Be it known that I, EDWARD C. WALKER, 3d, a citizen of the United States, and resident of Brookline, in the county of Norfolk and State of Massachusetts, have invented new and useful Improvements in Methods of Electrolytic Production of Perchloric Acid,

of which the following is a specification.

7 It has been known for a long time that perchlorates are .formed by electrolysis of chlorids, and that perchloric acid (HClO or 'ClO OI-I) can be produced in small amounts" by oxidation of hydrochloric acid during electrolytic decomposition of solutions thereof. Heretofore, however, so far as I am informed and have been able to ascertain,.the quantity of perchloric acid obtainable by electrolysis, under known conditions, has

been so small that no approximation to practical commercial production has been attained. By my process herein described and claimed, perchloric acid is produced with economy consistent with. commercial requirements.

Variable factors in electrolytic production of perchloric acid, which influence the rate, quantity, and economy of manufacture, are: (1) duration of electrolysis; (2) current-density; (3) concentration of the acid electrolyte; (4) temperature; (5) anode ma ,terial.

In respect to these variable factors, my

process is characterized by the following conditions: w (1) The. duration, of electrolysis is influenced by the other four variable factors, (as illustrated by the table hereinbelow)... but under given conditions the electrolysis is continued until ractically all the hydro chloric acid has disappeared from the solu- Speciflcation of Letters Patent.

- Patented July 9, 1918.

tion and until practically all the chloric acid has been electrolytically oxidized-to perchloric acid. Upon concentrating this electrolyzed solution, pure perchloric acid is obtained, since the hydrochloric and chloric acids are. evaporated OE With the' excess water.

' (2) The current-density on the anode has a range from one-tenth to five-tenths ampere per square centimeter, preferably not more than three-tenths for highest efficiency.

(3) The hydrochloric acid electrolyte has a range of concentration from one-tenth nor mal to one normal.

about 0 C. to about 50 C.; but for efficient production of perchloric acid, temperatures at the 1ower end of this range-should be maintained, especially during the later stages of the process, as will presently be explained. I Y

' (5) As anode materials carbon or graphite, fused magnetite, or platinum are available. Carbon may be used for the intermediate oxidation of hydrochloric acid to chloric acid but, by reason of the lowovervoltage of oxygen on this material, plati- (4) The temperature may range from num or fused magnetite is preferably to be used for the complete oxidation of ch10 ric acid to perchloric acid. For a chemi- Duration of electrolysis 4 ampere-hours.

Current density 0. 102 0. 137 0. 171 0. 204 I v v H01 at start 0984 0984 251 510 0984 0984 251 R01 present at end 014 ampere-hours 0123 0138 050 160 I 015? 0157 057 Per cent. 3131 present ,i 12. 5 14. 0 19. 9 31. 4 15. 5 l6. 0 22. 7- Per cent. H01 lost. 44. 0 41. 2 59. 0 r 60. 9 38. 9 38. 8 57. 0 Per cent. H61 converted to H010 3.10 1. 50 5. 38 6. 45 60 2. 15

1 Per cent. H01 converted to H0104. 41. 6 43. 0 15. 0 2. 36 45. 0 44. 0 17. 9

Eq! 11010, per liter 0031 0015 0135 0329 0006 0054 Eq.* H010 per liter 0410 0423 0370 0120 0443 0433 0450 Watt hours per gram H0104 42. 0 47. 4 39. 8 97. 2 0 58. 5 40. 5

* Equivalent to.

' H01 present at end of 7 ampere-hours .Per cent. HCl converted to H0104 Current density HClat start Per cent. HCl resent. Per cent. H01 lbst. Per cent. H01 converted to H010;

E H010 r liter....' E854 noidl ier liter Watt hours per gram H0104 Duration of electrolysis 7 amperehours.

* Eqsiliivalent to. [It s ould be noted that in obtaining the above data, 150 com. of acid was electrolyzed under the conditions specified and then anprocess herein described.]

My investigations justify the conclusion, that'reasonably, or commercially ecorromlcal production of perchloric acid is conditioned upon dilutionof the hydrochloric acid elec freezing point of the electrolyte'and is practically 0 (3., since water is the best available agent for cooling the electrolytic cell.

' Since'the formation of the intermediate product-chloric acid-takes place with the greatest efliciency of temperatures ranging from 25 C. to 0., in solutions of hydrochloric acid whose concentrations .lie within the higher specified range,- and with the lower current densities; and whereas the lower temperatures and higher current densities are more favorable to the subsequent oxidation of chloric acid to per-chloric acid, the process may with appreciable technical advantage be characterized by maintenance of the higher temperatures, lower current densities, and higher concentrations of hydrochloric acid during the early stages, and subsequent depression of temperature, and increase in current density. 'As the transition-of product from I-IClO to H010 is gradual rather than abrupt, the stage when the temperature will advantageously be lowered will be ascertained by examination of samples of solution, taken from time to time, and obviously will vary with variations of the factors involved. vFor practical and commercial purposes, however, the

electrolysis should be continuous, and may be carried out so as to take advantage of the above stated facts by using an apparatus as is illustrated in the drawings annexed, in wh1ch Figure 1 is a diagrammatic representation of the apparatus;

Fig. 2 is a side elevation of one of the electrolysis cells;

Fig. 3 is a top plan view of the cell; and

v Fig. 1 is an end elevation of the cell.

Referring to Fig. 1 'A is the tank holding the supply of dilute HCl used as the elecalyzed. Thus the process was not strictly continuous, and the tab ulated results are all relatively lower thanthose for the continuous trolyte. B is the first electrolyzing unit which is maintained at the'proper temperature in the higher range, and in which (1) is the platinum, magnetite, or carbon anode of such dimensions as to give the proper current density. The tank itself (2) is constructed of copper with a silver lining, and serves as the cathode. The cooling may be efi'ected by spraying the cooling water (by means not shown) on the outside of the tank B. The flare (9) at the topof the tank is desirable to resist the corrosion at the junction of liquid and air due to the evolved chlorin gas, and gives this protection because of the presence of a stream of hydrogengas which is always between it and the active chlorin.

(4:) is a siphon overflow which maintains thelevel of the liquid B at the correct point. It is constructed of,silver where it emerges from the tank, and a glass joint is made at the point G, the rest of the siphon being of glass. This construction is necessary as nometal except platinum will withstand the chlorin gas dissolved in the solution passing through the apparatus unless protected by evolution of cathodic hydrogen.

The unit C is similar to unit B, and is maintained within the lower temperature range, so as to produce HClO at highest efliciency from the HCIO which exists in high concentration in the solution enterg G77. I

.(3) is an anode either of'platinum or fused magnetic iron oxid, of such size as to give the proper high current density.

(6) is another siphon overflow similar to (4:) and empties into the tank D.

From tank D the electrolyzed solution passes through a valve (7) into a fused silica cascade evaporator E and F.

The solution flowing into receptacle R is nearly pure perchloric acid of concentration up to 60%.

In Figs. 2, 3 and 4, the cell 2,'with flar- .ing top 9, is shown. The preferred construc- U tion and dimensions are; that the cell should be of seamless copper, lined with silver,

eighteen inches long, one inch -wide,-and five inches high to the flare 9; width at the top of the flare three inches.

Anapparatus comprising units B and C of the dimensions shown in the detail drawing will produce approximatelythree (3) pounds of 60% perchlorieacid in twenty-four hours operation.

What I claim and desire to secure by Letters Patent is:

1. The process of producing perchloric acid, which consists in subjecting to electro lytic action a hydrochloric acid solution, strgngth one normal, or less, with currentdensity at five-tenths ampere, or less, per square centimeter. v

2. The process of producing perchloric acid, which consists in subjecting to electrolytic action a hydrochloric acid solution,

strength. one normal, or less, with currentdensity at five-tenths ampere, 'or less, per square centimeter,'at a temperature not aterially exceeding 50 centigrade.

3.- The processv of producing perchloric acid, which consists in subjecting to electrolytic action a hydrochloric acid solution, strength one normal, or less, with currentdensity at five-tenths ampere, or less, persquare centlmeter, at a temperature not materially exceeding 50 centigrade at the initial stages of the process, and reducing the temperature as the process progresses.'

temperature not -centigrade, in the'initial stage, and at ma- 4. The process of producing perchloric acid, which consists in subjecting to success1ve stages of electrolytic action a hydrochloric acid solution, strength one -normal or less, with current-density atfive-tenths ampere or less per 5 uare centimeter, at a aterially exceeding 50 sive stages of electrolytic action a hydro chloric acid solution, strength one normal or less, with current-density at five-tenths ampere or less per square centimeter, at a temperature not materially exceeding50 centigrade, in the initial stage, and at mate- -rially reduced temperature in a subsequent electrolyte stage, maintaining flow of through the initial stage, to and through the subsequent stage, drawing oil and concentrating the perchloric acid solution thus produced.

electrolyte Signed by me at Bost n, Massachusetts,

this 14th day of A.pril,19 7.

\ EDWARD o. WALKER, III. 

